San Diegans are pondering that question after grass-roots preservationists defeated billionaire Irwin Jacobs’ $45 million plan to remove cars and traffic from the middle of Balboa Park.

There’s concern that a court ruling against Jacobs’ plan could discourage philanthropists from making large donations to civic projects, especially in cases where they expect to have a major say in how their money is spent.

The idea is dismissed by activists who say the decision merely shows that the Qualcomm founder pushed a plan that left no room for compromise.

Still, for the first time in modern San Diego history, San Diego said no to a public-spirited billionaire, a man ranked 311th on Forbes 400 list of the wealthiest Americans. Jacobs, 79, gave $120 million each to the San Diego Symphony and to UC San Diego’s engineering school, where he taught in the 1960s. He and his wife Joan continue to give away their $1.5 billion fortune to many causes.

Jacobs said he was “saddened” that his plan, conceived three years ago, to make the Plaza de Panama and other spaces pedestrian-only in time for the park’s 2015 centennial celebration has been rejected.

He said he’ll redirect the $30 million he was prepared to donate to other causes in other places.

Some people are dismayed that the judge’s decision, pegged to a technicality in city law, will have long-term implications for other civic endeavors — that it will chill the enthusiasm of otherwise generous do-gooders.

Others see the turnabout as an opportunity to forge compromise between big moneyed and powerful political interests with grass-roots groups and neighborhood activists.

However, until a new spirit of cooperation takes hold, donors like Darlene Shiley say they will direct their funds elsewhere. Her charities to universities, the arts, health and public television are made possible because of the fortune whose late husband Donald built after inventing the artificial heart valve.

“When you have someone as well respected as Irwin leading a project like this and you slam dunk him, that doesn’t bode well for future projects,” she said.

In light of higher taxes imposed at the state and national level, Shiley said there is less money available to share with worthy charities.

Benefactors will continue to support nonprofits, but city projects will face a tougher sell, she said.

“It’s hard to trust the government agencies as it is. When something like this happens, it’s tough to get past it.”

Diane Coombs, a veteran activist of many environmental and planning battles, said the Jacobs defeat signals a new era in which big ideas backed by big wallets and political power must pass muster with the general public.

In the Plaza de Panama case, she said Jacobs aimed too high to solve a bigger problem when it was just the cars in that plaza that needed to go away, at least to begin with.